not so long ago, alchemists dreamed of turning cheap and ugly metals into valuable ones like gold. Power plants (also called power stations) pull off a similar trick, converting lumps of coal and drops of oil into zaps of electric current that can cook your dinner or charge your phone. If it weren’t for power plants, I wouldn’t be writing these words now—and you wouldn’t be reading them. In fact, most of the things we do every day and much of the stuff we use owes a hidden debt of gratitude to these gigantic energy factories, which turn “fossil fuels” (coal, natural gas, and oil) into electric power.

This energy-alchemy is a pretty amazing trick—and quite a recent one too, since the very first practical power station was built in only 1882 (by Thomas Edison). Yet amazement is often the last thing we feel when we think about generating electricity at the start of the 21st century. In an age when caring for the environment is (quite rightly) more important than ever, it’s fashionable to sneer at power plants as evil, dirty places pumping pollution into our air, land, and water. One day, we might be able to make all our electricity in a completely clean and green way. Until then, power plants are vital for keeping our schools, hospitals, homes, and offices light, warm, and buzzing with life; modern life would be impossible without them. How do they work? Let’s take a closer look!

A single large power plant can generate enough electricity (about 2 gigawatts, 2,000 megawatts, or 2,000,000,000 watts) to supply a couple of hundred thousand homes, and that’s the same amount of power you could make with about 1000 large wind turbines working flat out. But the splendid science behind this amazing trick has less to do with the power plant than with the fuel it burns. The real magic isn’t that power plants turn fuel into electricity: it’s that even small amounts of fossil fuels contain large amounts of energy. A kilogram of coal or a liter of oil contains about 30MJ of energy—a massive amount, equivalent to a good few thousand 1.5-volt batteries! A power plant’s job is to release this chemical energy as heat, use the heat to drive a spinning machine called a turbine, and then use the turbine to power a generator (electricity making machine). Power plants can make so much energy because they burn huge amounts of fuel—and every single bit of that fuel is packed full of power.

Unfortunately, most power plants are not very efficient: in a typical old plant running on coal, only about a third of the energy locked inside the fuel is converted to electricity and the rest is wasted. Newer designs, such as combined cycle power stations (which we’ll explore in a minute) may be up to 50 percent efficient. As the chart here shows, even more electricity is squandered on the journey from the power plant to your home. Adding all the losses together, only about a fifth of the energy in the fuel is available as useful energy in your home.